Photo: Rodale

They have been referred to as "the world's simplest workout." They are incorporated into outdoor boot camp classes featuring unconventional exercises. And for as little as 50 cents, you can burn some serious calories with them.

Sandbags are hitting the fitness circuit by storm. When it comes to slimming down, getting stronger and toning up, this small item has big potential. Sandbags are simple and easy to use, easily adjustable to your level and the shifting weight of the sand challenges your body to expend more calories with each move.

Flexible enough for everyday athletes to professionals, some NFL players reportedly spend their off-season training with sandbags. "The ever-shifting shape of a sandbag makes it nearly impossible to settle into a lifting groove like you do with free weights or machines," head strength coach for the Tampa Bay Buccaneers told Men's Health. "So every workout is unique and challenging."

Most local hardware stores carry a basic, white sandbag with a tie string at the top for less than a dollar. Other outlets carry fancier bags with higher price tags, but I find the basic ones work just fine. They can be filled with store-bought sand or the real deal if you're lucky enough to live at the beach. Just you and one sandbag, and you're all set for a total body workout.

You can carry them, flip them, lift them and drag them. Basic moves include squats, lunges, curls, overhead presses and walking with the bag overhead. You can simulate rows, chops, jumps and twists. Get a group of people, and you can do line passes. Listen to the theme song from "Rocky" and do push-ups with the bag on your back.

I regularly work out with sandbags and love busting calories while I bust some moves with them. They add balance, core training, upper- and lower-body conditioning and some good 'ol toughness to my regimen. Plus, if I get an opportunity to work out at the beach or in my backyard vs. the gym, I'll take that any day.

Combined with a healthy diet, the possibilities for slimming down and toning up with sandbags are endless.

For more fitness inspiration, Men's Health talks about five muscles you can't ignore, how you can burn fat faster and scoring the best body ever.